"Application" example tries to save file even when you click cancel

To reproduce:

1. Start "application" example
2. Click "save" button to open the file dialog
3. Click "cancel"

You will get a message box that the file cannot be saved because the file name points to a directory.

Looking at the code in the example, it tries to detect cancel by checking if the returned list from selectedFiles() is empty. This is documented to never happen. The example should check the return value from exec() instead.

Reproduced on Linux and Android.